Always there to listen, Mari has helped Rika mature into a senior member. They always hang out, whether it be at the hot springs (which spawned the song Sotsugyou rouko ~Morning Musume tabitasu hito ni okuru uta~ from No.5) or yakiniku (which spawned the Yakiniku4 because Nono, Goto joined them) - Mari is one of Rika's closest friends.